Having made his purchase, the alleged violator--almost always a male according to city officials--will exit the store and find one of Cambridge's finest waiting for him. Once a purchase has been made, officers have the right to ask the buyer for ID.

If there's a fake ID in hand, citations are given out, and sometimes arrests are made.

And eager teens waiting for their overage buddy to buy them booze are warned to beware.

"[The police officer is] watching--and if the buyer hands it to the kids for a couple bucks...both will be arrested," says Frank D. Pasquarello, a Cambridge police department spokesperson.

On Cops in Shops's first weekend seven violators were nabbed, including 51-year-old Wilbert McCoy of Dorchester.

Authorities said McCoy bought liquor for two 15-year-old Cantabrigians.

He faced a judge the next morning, but most first-time offenders just face a fine of $200 or $300 and community service. Repeat offenders are jailed.

Surprise in Store

There are 39 stores city-wide that sell alcohol. Of them, 20 are exclusively purveyors of liquor and spirits--and thus face much tighter scrutiny from state and local officials, Pasquerello said.

"The majority of owners do not need any problems with liquor licensing," he said.

The other 19 stores--many of them in and around Harvard and Central Squares-are prime targets for prospective underage drinkers--and over the past year, for undercover cops.

That these stores have been helpful doesn't surprise Richard V. Scali, the executive director of the Cambridge's Licensing Commission.

"They've been very cooperative," he says. "We haven't had anybody whose been uncooperative. They've even been coming to our [Cambridge Licensing Board] meetings," he says.

But workers and managers at several of the stores, particularly in the area around Harvard Square, said their rapprochement with the city is reluctant.

"I won't sell cigarettes to a minor or anything like that," says Kerry Quikstrom, a manager of the Square's Store 24. "But I think it's ridiculous."